Green algae as a structural element of phytoperiphyton communities in streams of NW Russia

Observations were made on the development and distribution of phytoperiphyton communities in 66 lake-river systems in NW Russia from Lake Ladoga to the Barents Sea. In total, 130 genera and 648 species were identified from different substrates, belonging to Cyanophyta (19.1%), Bacillariophyta (59.6%), Chlorophyta (18.7%), and algae from other orders (2.6%). In all streams diatoms dominated by species richness, but they were surpassed by green algae in terms of biomass. The green algae ranged from small planktonic forms to large filamentous species and produced easily visible algal communities. Among the planktonic forms the desmids were the most diverse group. They occurred in attached communities of all rivers and, while never abundant, were widespread. The attached community’s biomass was dominated by green algae. Among these, the filamentous algae Mougeotia sp., Oedogonium sp., Zygnema sp., Spirogyra sp. and Ulothrix zonata exhibited mass development in streams. Their distribution was patchy in the basin, with a total cover varying from less than 1% to 90% of the stream bottom. In some river stretches the diversity and predominance of green algae could be due, in part, to poorly developed riparian canopies. The term periphyton adopted here follows the definition of Odum (1971): “Assemblages which include both plant and animal organisms growing attached to submerged objects”. The prefix phyto- is added to indicate that of the whole biocoenoses only phototrophs are considered in this study. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Early stages of biofilm succession in a lentic freshwater environment

Initial events of biofilms development and succession were studied in a freshwater environment at Kalpakkam, East Coast of India. Biofilms were developed by suspending Perspex (Plexiglass) panels for 15 days at bimonthly intervals from January 1996 to January 1997. Changes in biofilm thickness, biomass, algal density, chlorophyll a concentration and species composition were monitored. The biofilm thickness, biomass, algal density and chlorophyll a concentration increased with biofilms age and colonization was greater during summer (March, May and July) than other months. The initial colonization was mainly composed of Chlorella vulgaris, Chlorococcum humicolo (green algae), Achnanthes minutissima, Cocconeis scutellum, C. placentula (diatoms) and Chroococcus minutus (cyanobacteria) followed by colonial green algae such as Pediastrum tetras, P. boryanumand Coleochaete scutata, cyanobacteria (Gloeocapsa nigrescens), low profile diatoms (Amphora coffeaeformis, Nitzschia amphibia, and Gomphonema parvulum) and long stalked diatoms (Gomphoneis olivaceumand Gomphonema lanceolatum). After the 10th day, the community consisted of filamentous green algae (Klebshormidium subtile, Oedogonium sp., Stigeoclonium tenue and Ulothrix zonata) and cyanobacteria (Calothrix elenkinii, Oscillatoria tenuis and Phormidium tenue). Based on the percentage composition of different groups in the biofilm, three phases of succession could be identified: the first phase was dominated by green algae, the second by diatoms and the third phase by cyanobacteria. Seasonal variation in species composition was observed but the sequence of colonization was similar throughout the study period.     

Main biotic and climatic events in Early Permian of the Western Urals,Russia, as exemplified by the shallow-water biota of the early Kungurian lagoons

The paper deals with the Early Permian (mostly early Kungurian) biotas of the Cis-Urals (Perm region, Russia). Taxonomic composition of the early Kungurian biota of the stratotype area (close vicinity of the City of Kungur) includes algae Algites philippoviensis Naugolnykh, A. shurtanensis Naugolnykh, tracheophytes (higher plants), i.e., equisetophytes Paracalamites spp., conifers Shaidurodendron columnaris Naugolnykh, Walchia appressa Zalessky, vojnovskyaleans Rufloria derzavinii (Neuburg) S. Meyen etc.; invertebrates: coelenterates of uncertain affinity, bivalves Permophorus costatus (Brown), Permophorus sp., Netschajewia sp. cf. N. tschernyshowi (Licharew), gastropods Goniasma angulata (Stuckenberg), terebratulid brachiopods Dielasma sp. cf. D. moelleri Tschernyschew, arthropods (limulids Paleolimulus kunguricus Naugolnykh); vertebrates: chondrichthyan and actinistian fishes.Paleogeographically, the studied area belonged to the near-shore zone of a large lagoon basin disposed along the western-southern part of the Paleo-Urals during the Kungurian time. The main events in evolution of this basin reflect the final phases of the Artinskian sea basin with normal salinity, the transition to an early Kungurian (Philippovian) lagoon, then the appearance of intercalations of evaporate conditions and episodic incursion of marine faunas, and finally a gradual transition to semi-terrestrial environments with the cyanophyte communities in early Ufimian (Solikamskian, early Roadian) time. Climatic conditions in this area changed from semi-humid to semi-arid. A new genus and species of algae Dichothallus divaricatus Naugolnykh n. gen. n. sp. is described on the basis of material originated from the stratotype of the Philippovian Horizon of the Kungurian stage, Lower Permian.     

The influence of ultra-low temperatures on marine microalgal cells

The development of cryopreservation methods for microalgae opens great prospects for marine biotechnology and aims to establish a bank of cryopreserved cultures. Eight of ten marine microalgae species used in this study (the diatoms, green, red, and golden algae), including five previously untested species, were successfully recovered after freezing to ultra-low temperatures (?196 °C) using penetrating (dimethyl sulfoxide, glycerol, and ethylene glycol) and non-penetrating (trehalose and polyvinylpyrrolidone) cryoprotectants. We found that ethylene glycol in combination with trehalose possessed the most effective cryoprotective activity among the algae cryoprotectants tested. However, the chief factor for the successful preservation of microalgal cells during freeze–thawing was shown to be the cooling rate. Cooling was performed in two ways: step or fast droplet freezing. The droplet freezing described here was effective only for cryopreserving green algae, whereas step freezing was optimal for all other algal species. Three diatoms of the genus Attheya were successfully cryopreserved for the first time, but none of the tested protocols had a positive result for the diatoms belonging to Pseudo-nitzschia. The failure may be explained rather by peculiarities in the cell wall composition (higher content of silica and fewer organic components) than by the specific (long and thin) shape of these cells. The pigment content in all of the studied species tended to decrease after thawing as compared with unfrozen cells and increase significantly during cell recovery. Cryosensitivity of marine algae depended on the differences in natural intrinsic characteristics rather than their taxonomic position.     

Role of algae in the diet of Chironomus plumosus F. semireductus from the Bay of Quinte,Lake Ontario

The importance of algae and different algal species to the chironomid diet was investigated through examination of the guts of chironomids taken from 5 locations in Big Bay (Bay of Quinte, Lake Ontario) at 6 times during the ice-free period. A comparison of the density and condition of algal cells at the two ends of the gut provided information on the digestibility of each algal species and the algal biomass assimilated by the chironomids. Diatoms and two species of green algae were assimilated over much of the summer, but the blue green algae were digested only late in the season when their populations were aged and/or dying. In terms of energy contribution, diatoms, especially Stephanodiscus spp. and Melosira spp., were most important in May (99% of all algal biomass assimilated), August (98%), and Octobr (92%), while the blue green species, Microcystis aeruginosa, was predominant in September (76%). Only a few small greens were assimilated in June and July. The contribution of algae as a food source to chironomid energetics was small, and reached a maximum in August and September (15%–34%). It is postulated that bacteria are a more important food source.     

DIATOM COMMUNITIES FROM A DELAWARE SALT MARSH 1,2

Edaphic diatoms were collected from 5 representative habitats of Canary Creek salt marsh, Lewes, Delaware, from 24 July 1969 to 21 July 1970. Of the 104 taxa encountered, 32 had a general distribution on the marsh and 41 were endemic to one of the 5 habitats sampled. Three of the habitats supported stands of grasses: tall Spartina alterniflora Loisel., dwarf S. alterniflora, and Distichlis spicata (L.) Greene; and these habitats possessed the highest species diversity (H') and the greatest number of diatom species. The remaining 2 habitats, a bare bank and a panne, were devoid of macroscopic vegetation. The diatoms of these last 2 habitats were exposed to hypersaline conditions during warmer periods of the year and this was considered a contributing factor to the lower values observed for the aforementioned parameters of community structure. A comprehensive examination of the community structure characterizing the 5 habitats, employing statistical analyses and the distribution of species, showed each habitat to support its own unique and easily recognizable edaphic diatom community. A multiple regression analysis indicated that the differences between the 5 communities were closely related to differences in temperature and elevation between the habitats, and also a result of significant interactions between edaphic diatoms and filamentous algae.     

The radiation of spring snails of the genus Belgrandiella in Austria (Mollusca: Caenogastropoda: Hydrobiidae)

Grain density microautoradiography (MAR) was used to study uptake of dissolved amino acids (DFAA) in microalgal communities from a sandy bay on the west coast of Sweden. A mixture of fifteen ³H-labeled amino acids (final concentration 20–80 nmol l^–1) was added to sediment samples collected from two depths (0.5 and 4 m), on five occasions representing different seasons. On all sampling occasions, the microflora was dominated by diatoms (> 85% of the total biomass). Cyanobacteria occurred in the summer and autumn, but never dominated the biomass. Between 5 and 48% of all counted algal cells showed uptake (1–44% of algal biomass). Uptake was recorded for all majors microalgal groups (diatoms, cyanobacteria and autotrophic flagellates). Uptake was more frequent on the shallow site and the highest proportion of cells showing uptake occurred in May. Although uptake was common among both motile and attached growth forms, on several occasions uptake frequencies were higher for attached cells. As the attached fraction is frequently burried out of the photic zone, and not able to rapidly migrate towards light, this implies that heterotrophic capacity should be valuable. Also at species level, some taxa showed higher uptake frequencies than others, for example populations of motile diatom species that displayed a seasonal behaviour (blooming species), such as Nitzschia cf. dissipata and Cylindrotheca closterium. Other species showing frequent uptake were the coccoid colony-forming cyanobacterium Microcrocis sp., and the filamentous cyanobacterium Phormidium sp.. The results suggest that there is a high potential for DFAA uptake in the microphytobenthic community and that for some growth forms and species this could imply a competitive advantage.     

Bacterial communities of some brown and red algae from Peter the Great Bay, the Sea of Japan

The structure of microbial communities of brown algae, red algae, and of the red alga Gracilaria verrucosa, healthy and affected with thallus rot, were comparatively investigated; 61 strains of heterotrophic bacteria were isolated and characterized. Most of them were identified to the genus level, some Vibrio spp., to the species level according to their phenotypic properties and the fatty acid composition of cellular lipids. The composition of the microflora of two species of brown algae was different. In Chordaria flagelliphormis, Pseudomonas spp. prevailed, and in Desmarestia viridis, Bacillus spp. The composition of the microflora of two red algae, G. verrucosa and Camphylaephora hyphaeoides, differed mainly in the ratio of prevailing groups of bacteria. The most abundant were bacteria of the CFB cluster and pseudoalteromonads. In addition, the following bacteria were found on the surface of the algae: Sulfitobacter spp., Halomonas spp., Acinetobacter sp., Planococcus sp., Arthrobacter sp., and Agromyces sp. From tissues of the affected G. verrucosa, only vibrios were isolated, both agarolytic and nonagarolytic. The existence of specific bacterial communities characteristic of different species of algae is suggested and the relation of Vibrio sp. to the pathological process in the tissues of G. verrucosa is supposed.     

A metabarcoding comparison of windward and leeward airborne algal diversity across the Ko‘olau mountain range on the island of O'ahu,Hawai‘i1

Airborne algae from sites on the windward (n = 3) and leeward (n = 3) sides of the Ko‘olau Mountain range of O‘ahu, Hawai‘i, were sampled for a 16 d period during January and February 2015 using passive collection devices and were characterized using Illumina MiSeq sequencing of the universal plastid amplicon marker. Amplicons were assigned to 3,023 operational taxonomic units (OTUs), which included 1,189 cyanobacteria, 1,009 heterotrophic bacteria, and 304 Eukaryota (of which 284 were algae and land plants). Analyses demonstrated substantially more OTUs at windward than leeward O‘ahu sites during the sampling period. Removal of nonalgal OTUs revealed a greater number of algal reads recovered from windward (839,853) than leeward sites (355,387), with the majority of these being cyanobacteria. The 1,234 total algal OTUs included cyanobacteria, diatoms, cryptophytes, brown algae, chlorophyte green algae, and charophyte green algae. A total of 208 algal OTUs were identified from leeward side samplers (including OTUs in common among samplers) and 1,995 algal OTUs were identified from windward samplers. Barcoding analyses of the most abundant algal OTUs indicated that very few were shared between the windward and leeward sides of the Ko‘olau Mountains, highlighting the localized scale at which these airborne algae communities differ. Back trajectories of air masses arriving on O‘ahu during the sampling period were calculated using the NOAA HY‐SPLIT model and suggested that the sampling period was composed of three large‐scale meteorological events, indicating a diversity of potential sources of airborne algae outside of the Hawaiian Islands.     

The independent and interactive effects of snail grazing and nutrient enrichment on structuring periphyton communities

We investigated the independent and interactive effects of nutrient enrichment and snail grazing on structuring periphyton communities in a northern temperate lake. Nutrient releasing substrates and grazer enclosures were used to simultaneously manipulate nutrient availability and herbivory. Periphyton was allowed 18 days to accrue before grazers (Elimia livescens = Goniobasis livescens) were introduced.Addition of nitrogen and phosphorus caused a significant increase in biovolume (p < 0.001), whereas grazing had no significant effect on biovolume but resulted in a shift in species composition. Four taxa were largely responsible for the increase in biovolume on the nutrient enriched substrates: Oedogonium sp, Stigeoclonium tenue, Navicula radiosa var. radiosa and Navicula radiosa var. tenella. By the 28th day, nutrient enrichment caused a shift from a community dominated by diatoms (Bacillariophyceae) to a community dominated by green algae (Chlorophyceae). Blue green algae (Myxophyceae) maintained an equal proportion in high and low-nutrient regimes.Grazing had a more pronounced effect on altering community composition on the nutrient enriched substrates than on the unenriched substrates. Grazing caused a decrease in diversity and an increase in dominance by green algae on the nutrient enriched substrates. The relative biovolume of green algae increased from 64% to 93% on grazed substrates, due to the significant increase in relative abundance of Stigeoclonium tenue. This taxon has both prostate basal cells and erect filamentous cells. The ratio of basal: filamentous cells increased from 4.7 to 5.2 with grazing, suggesting that the heretotrichous growth form of Stigeoclonium tenue is adapted to grazing by virtue of the basal cells which are able to adhere to the substratum and resist being grazed.     

THE DISTRIBUTION OF EDAPHIC DIATOMS ALONG ENVIRONMENTAL GRADIENTS OF A LOUISIANA SALT MARSH1

Edaphic (sediment-associated) diatoms were collected from five sites along a gradient from slightly brackish to saline marsh on 30 November 1977 and 29 April 1978. Several environmental factors change along this gradient in addition to salinity, including tidal flushing and percent organic content of the soil. A total of 112 taxa were identified, with Amphora exigua Greg., Navicula phyllepta Kütz., N. salinarum Grun., and N. tripunctata (Müll.) Bory being among the five most abundant taxa on both sampling dates. The taxonomic composition of the diatom flora was very similar to those observed for other salt marshes located along the Gulf and Atlantic coasts. Diatom taxa were generally euryhaline and distributed continuously along the gradient from brackish to saline marsh. Species diversity (H¹) and the number of taxa in a sample (S) were also similar to those reported for other North American salt marshes. The number of taxa in a sample was higher in the saline than in the brackish area on both sampling dates while species diversity was greater in the saline area only in April.     

Production stability and biomass quality in microalgal cultivation – Contribution of community dynamics

The prospect of using constructed communities of microalgae in algal cultivation was confirmed in this study. Three different algal communities, constructed of diatoms (Diatom), green algae (Green), and cyanobacteria (Cyano), each mixed with a natural community of microalgae were cultivated in batch and semi‐continuous mode and fed CO₂ or cement flue gas (12–15% CO₂). Diatom had the highest growth rate but Green had the highest yield. Changes in the community composition occurred throughout the experiment. Green algae were the most competitive group, while filamentous cyanobacteria were outcompeted. Euglenoids, recruited from scarce species in the natural community became a large part of the biomass in semi‐steady state in all communities. High temporal and yield stability were demonstrated in all communities during semi‐steady state. Valuable products (lipids, proteins, and carbohydrates) comprised 61.5 ± 5% of ash‐free biomass and were similar for the three communities with lipids ranging 14–26% of dry mass (DM), proteins (15–28% DM) and carbohydrates (9–23% DM). Our results indicate that culture functions (stability, biomass quality) were maintained while dynamic changes occurred in community composition. We propose that a multispecies community approach can aid sustainability in microalgal cultivation, through complementary use of resources and higher culture stability.     

Periphytic and drifting microalgae in a tributary stream of Øvre Heimdalsvatn

Samples of drifting and periphytic microalgae were collected during 1972 from a fast-flowing, stony stream (Brurskardsbekken) in the Jotunheimen mountain area, central southern Norway. The predominant algal groups in the drift and the periphyton were diatoms and green algae, while only a few species were recorded in both communities. A considerable number of species from Chrysophyceae, Cryptophyceae and other algal classes were also recorded in the drift samples. The species composition was in good agreement with microalgal communities earlier described from mountain areas in Scandinavia, although species which probably are new to Norway, were also recorded. A quantitatively important fraction of planktonic species in the drift is interpreted as a contribution from lacustrine habitats in the watercourse. A general change in the periphyton during the summer, from green algae to diatoms, was observed, Altitudinal differences in the periphyton included a delayed green algal maximum at higher altitudes compared to lower. In the zone around the upper birch limit, a transition in species composition as one goes up stream, described in other investigations, was not observed.     

Epiphytic diatom communities on intertidal seaweeds from Iceland

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm⁻². Erect growth forms were the most abundant, representing on average 50% of the total diatoms (Achnanthes cf. brevipes var. parvula, Tabularia investiens, T. fasciculata, Hyalosira cf. delicatula, Gomphoseptatum aestuarii, Pseudogomphonema plinskii), followed by adnate (29%) (Cocconeis stauroneiformis, C. scutellum) and motile forms (21%) (Nitzschia cf. amphibia and Navicula perminuta). Highly branched seaweeds with articulated thallus surface, offering a number of microenvironments to be occupied by the epiphytes, showed a high level of colonization, mainly due to erect and motile diatoms. Flat thalli with smooth surface allowed for the growth of mainly erect diatoms.     

Phyllosphere eukaryotic microalgal communities in rainforests: Drivers and diversity

Phyllosphere algae are common in tropical rainforests, forming visible biofilms or spots on plant leaf surfaces. However, knowledge of phyllosphere algal diversity and the environmental factors that drive that diversity is limited. The aim of this study is to identify the environmental factors that drive phyllosphere algal community composition and diversity in rainforests. For this purpose, we used single molecule real-time sequencing of full-length 18S rDNA to characterize the composition of phyllosphere microalgal communities growing on four host tree species (Ficus tikoua, Caryota mitis, Arenga pinnata, and Musa acuminata) common to three types of forest over four months at the Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. Environmental 18S rDNA sequences revealed that the green algae orders Watanabeales and Trentepohliales were dominant in almost all algal communities and that phyllosphere algal species richness and biomass were lower in planted forest than in primeval and reserve rainforest. In addition, algal community composition differed significantly between planted forest and primeval rainforest. We also found that algal communities were affected by soluble reactive phosphorous, total nitrogen, and ammonium contents. Our findings indicate that algal community structure is significantly related to forest type and host tree species. Furthermore, this study is the first to identify environmental factors that affect phyllosphere algal communities, significantly contributing to future taxonomic research, especially for the green algae orders Watanabeales and Trentepohliales. This research also serves as an important reference for molecular diversity analysis of algae in other specific habitats, such as epiphytic algae and soil algae.     

Physiological responses of estuarine phytoplankton to ultraviolet light-induced fluoranthene toxicity

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants associated with urbanization and suburbanization in estuarine systems, but little is known about their effects on the physiological properties of microalgae. We examined the effects of ultraviolet (UV)-activated fluoranthene toxicity on (a) the growth, chlorophyll a content cell⁻¹, and pigment composition of axenic Ankistrodesmus sp. (an estuarine benthic green microalga) and (b) the phytoplankton population growth and pigment composition of natural communities from an urbanized (Murrells Inlet) vs. forested (North Inlet) salt marsh estuary. The zeaxanthin/violaxanthin ratio increased in Ankistrodesmus sp. cultures exposed to UV light in the presence of fluoranthene, supporting the hypothesis that xanthophyll cycling is an energy dissipative response to photoinduced PAH toxicity in this species. Exposure of natural communities to the combination of UV light and fluoranthene resulted in decreased chlorophyll production and increased zeaxanthin violaxanthin⁻¹ in samples from the urbanized estuary (Murrells Inlet), but not North Inlet, suggesting that phytoplankton in the former “fluoranthene-impacted” estuary were more susceptible to fluoranthene toxicity. Consideration of xanthophyll cycling as a microalgal response to UV-activated PAH toxicity has implications to understanding the influence of these contaminants on microbial food web structure and ecosystem production.     

Invasive reed effects on benthic community structure in Lake Erie coastal marshes

We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared macroinvertebrate densities among patches (0.25 m²) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone has little effect on the H′-diversity–reed dominance relationship.     

Biogeography of salt marsh plant zonation on the Pacific coast of South America

Aim

The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large‐scale variation in salt marsh plant community structure.

Location

A 2,000‐km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper‐arid at low to hyper‐humid at high latitudes.

Methods

Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large‐scale variation in salt marsh plant community structure.

Results

Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper‐arid and semi‐arid climates, but not in arid, humid and hyper‐humid climates. Latitudinal variation in low‐marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances.

Main conclusions

Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change.     

Spatial distribution of epiphytic chironomid larvae in a shallow macrophyte-dominated lake: effect of macrophyte species and food resources

Four submerged macrophytes were analysed with their respective assemblages of chironomid and algal taxa. Studies were made bimonthly, from January to November, in a shallow macrophyte-dominated lake. The periphytic algal community was represented by chlorophytes, diatoms and cyanobacteria; diatoms showed the highest relative abundance on the macrophyte species during the study. Algal biomass was affected by the season, and in January the highest values were found on Stratiotes aloides L., Potamogeton lucens L., Myriophyllum spicatum L.; in July on Chara aculeolata Kütz. The lowest algal biomass, on most of the macrophytes studied, was found in September. Larvae of Dicrotendipes sp., Diplocladius cultriger Kieffer, Endochironomus albipennis gr., Endochironomus impar (Walker), Glyptotendipes sp. and Paratanytarsus austriacus Kieffer were dominant within the chironomid community. The spatial distribution of chironomids between macrophytes species was related to periphytic algae biomass and certain environmental variables (temperature, water transparency, biomass of chlorophytes and diatoms). Analysis of chironomid diet and the results of canonical correspondence analysis confirmed this relationship. The strongest chironomid-algae relationships were observed on S. aloides and P. lucens.     

Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay,western Antarctic peninsula

Diatoms are one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula (WAP). Although generally well‐studied, little is known about size dependent photophysiological responses in diatom bloom formation and succession. To increase this understanding, four Antarctic diatom species covering two orders of magnitude in cell size were isolated in northern Marguerite Bay (WAP). Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, Thalassiosira cf. antarctica, and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixation, and growth were assessed. The small species Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyll cycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica. Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibition and photoprotection and carbon fixation showed no relationship with cell size. This study supports the dominance of small diatoms at low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatoms during the phytoplankton bloom in the WAP. This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatom bloom formation.